Surgically implanted cardiac pacing systems, such as pacemakers and defibrillators, play an important role in the treatment of heart disease. In the 50 years since the first pacemaker was implanted, technology has improved dramatically, and these systems have saved or improved the quality of countless lives. Pacemakers treat slow heart rhythms by increasing the heart rate or by coordinating the heart's contraction for some heart failure patients. Implantable cardioverter defibrillators stop dangerous rapid heart rhythms by delivering an electric shock.
Cardiac pacing systems typically include a timing device and a lead, which are placed inside the body of a patient. One part of the system is the pulse generator containing electric circuits and a battery, usually placed under the skin on the chest wall beneath the collarbone. To replace the battery, the pulse generator must be changed by a simple surgical procedure every 5 to 10 years. The other parts are the wires, or leads, which run between the pulse generator and the heart. In a pacemaker, these leads allow the device to increase the heart rate by delivering small timed bursts of electric energy to make it beat faster. In a defibrillator, the lead has special coils to allow the device to deliver a high-energy shock and convert dangerous rapid rhythms (ventricular tachycardia or fibrillation) back to a normal rhythm. The leads transmit information about the heart's electrical activity to the pacemaker.
For both of these functions, leads must be in contact with heart tissue. Most leads pass through a vein under the collarbone that connects to the right side of the heart (right atrium and right ventricle). In some cases, a lead is inserted through a vein and guided into a heart chamber where it is attached with the heart. In other instances, a lead is attached to the outside of the heart. To remain attached to the heart muscle, most leads have a fixation mechanism, such as a small screw and/or hooks at the end. Within a few months, the body's natural healing process forms scar tissue along the lead and at its tip, which fastens it even more securely in the patient's body, thereby complicating removal or extraction of the pacing lead. Leads usually last longer than device batteries, so leads are simply reconnected to each new pulse generator (battery) at the time of replacement.
Although leads are designed to be implanted permanently in the body, occasionally these leads must be removed, or extracted. The most common reason for lead extraction is infection. If any part of the system becomes infected, it is usually impossible to cure the infection without completely removing all hardware from the body. This requires removal both of the pulse generator from the chest wall and all leads from the veins and heart. Another reason for lead extraction is when a lead fails to work properly (for example, due to a break in the metal wire or surrounding insulation). Sometimes, the broken lead can be abandoned in the heart, with a new lead placed alongside. However, veins can only accommodate a limited number of leads due to space constraints, and sometimes, nonfunctioning leads must be extracted to make space for a new lead.
A variety of tools have been developed to make lead extraction safer and more successful. Current pacing lead extraction techniques include mechanical traction, mechanical devices, and energy devices. Some mechanical devices use a wire dial passes down the length of the lead, locking into place and allowing force to be applied to the tip of the lead. Another mechanical tool is a flexible tube called a sheath that passes over the lead, surrounding it and freeing it from the body by disrupting scar tissue as it is advanced toward the heart. Another mechanical tool uses a mechanical cutter to break through the scar tissue. Dilating telescopic sheaths can be used to strip or push away the scar tissue adhering the lead to the body. Energy devices, known as power sheaths, typically apply a form of energy at the sheath tip to cut the scar tissue away from the lead thus allowing for removal. As the sheath is pushed over the lead and comes to an area of attachment, the operator can turn on the sheath's energy source to heat or vaporize scar tissue. This has the effect of cutting the lead from its attachments, allowing the lead to be removed safely with much less force. One of these specialized sheaths uses electrocautery, similar to what is used to cut through tissue in surgery. Another commonly used sheath has a ring of tiny lasers at its tip. When activated, the lasers vaporize water molecules in scar tissue within 1 mm, which allows the sheath to be passed slowly over the entire lead until it can be removed. Occasionally, leads cannot be extracted from the chest and are instead removed through the femoral vein in the groin by use of specialized tools.
In any of the above lead removal devices and techniques, a damaged outer insulation layer of the lead can weaken the lead, which is often under significant tension or pull forces needed to assist its removal. In addition to lead damage from defective manufacture or lead implantation, leads can be perforated or cut during lead removal. Once the lead insulation layer is compromised, the remaining insulation layer can tear, and the inner conductive structures unravel.